Natural volatiles impair the response of Hylobius abietis adults to synthetic attractants in Norway spruce clear cut areas

For over 20 years it has been known that mature adults of Hylobius abietis are attracted by the combination of alpha-pinene and ethanol. However, it is not clear to what extent weevil response to these stimuli is influenced when large quantities of similar volatile substances are present in the environment, and how the response depends on the release rate of volatile substances from traps. Nothing that, in fresh Norway spruce clear-cuttings, the mature weevils were equally attracted to the traps baited with dispencers having different release rates, we assumed that the experiment results were affected by the abundance of natural volatile substances issued from the fresh slash, which masked the differences between olfactory signals released from traps. To verify this hypothesis, the experiment conducted in fresh clear-cuttings was repeated in exactly the same place after almost a year, when the overground slash were old. For seven weeks, at the beginning of growing season 2008, in two experimental areas, 6 different combinations of alpha-pinen and ethanol were tested using the traps buried in the soil. In both experimental area was captured about the same number of weevils and catch dynamics were similar. In the first two weeks of experimentation, when there were the highest captures, but also for the entire period of experimentation, there were significant differences between the tested variants in what concerns the average number of captures, the traps baited with dispenser providing higher release rate of ethanol and alpha-pinene having higher catches. This shows that in the first season of vegetation the weevil response to the attractants was affected by the profusion of similar volatile substances issued from natural sources (fresh cutt stumps, branches, foliage, bark etc.).